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Aminolevulinic acid synthase
ALA synthase (), or ALAS, catalyzes the synthesis of D-Aminolevulinic acid (ALA) the first common precursor in the biosynthesis of all tetrapyrroles such as hemes, cobalamins and chlorophylls.〔Hunter, Gregory A. Molecular enzymology of 5-Aminolevulinate synthase, the gatekeeper of heme biosynthesis http://www.sciencedirect.com/science/article/pii/S1570963911000021〕 The enzyme is expressed in all non-plant eukaryotes and the α-class of proteobacteria. Other organisms produce ALA through a three enzyme pathway known as the Shemin pathway. ALA is synthesized through the condensation of glycine and succinyl-CoA. In humans, transcription of ALA synthase is tightly controlled by the presence of Fe2+-binding elements, to prevent accumulation of porphyrin intermediates in the absence of iron. There are two forms of ALA synthase in the body. One form is expressed in red blood cell precursor cells (ALAS2), whereas the other (ALAS1) is ubiquitously expressed throughout the body. The red blood cell form is coded by a gene on chromosome x, whereas the other form is coded by a gene on chromosome 3. The disease X-linked sideroblastic anemia is caused by mutations in the ALA synthase gene on chromosome X, whereas no diseases are known to be caused by mutations in the other gene. Gain of function mutations in the erythroid specific ALA synthase gene have been shown recently to cause a previously unknown form of porphyria known as X-linked-dominant protoporphyria.
==Enzyme Structure and Properties==
PLP-dependent enzymes are prevalent because they are needed to transform amino acids into other resources.〔Molecular enzymology of 5-Aminolevulinate synthase, the gatekeeper of heme biosynthesis http://www.sciencedirect.com/science/article/pii/S1570963911000021〕 ALAS is a homodimer with similarly sized sub units and the active sites consisting of amino acid side chains such as arginine, threonine, and lysine exist at a subunity interface.〔Molecular enzymology of 5-Aminolevulinate synthase, the gatekeeper of heme biosynthesis http://www.sciencedirect.com/science/article/pii/S1570963911000021〕 The protein when extracted from R. spheroids contains 1600-folds and weighs about 80,000 daltons.〔d-AminoLevulinic Acid in Plants: Its Biosynthesis, Regulation, and Role in Plastid Development http://www.annualreviews.org/doi/pdf/10.1146/annurev.pp.29.060178.000523〕 Enzymatic activity varies for different sources of the enzyme.〔d-AminoLevulinic Acid in Plants: Its Biosynthesis, Regulation, and Role in Plastid Development http://www.annualreviews.org/doi/pdf/10.1146/annurev.pp.29.060178.000523〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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